Non-hysteretic, repeatable, and substantially linear responses of the sensor and shields (S1 and S2) are to be preferred in a magnetic read-write head. The key contributors are to such nonlinear and hysteretic responses are uncontrolled magnetic domains in the shields. Examples relating to various shield domain configurations are shown in FIGS. 1-3. Originally obtained as micro-Kerr images, they are presented here as line drawings, in the interests of improved clarity. These responses are typical of what is seen in the prior art.
The current (prior art) design standard for shields is to give them a rectangular (or close to rectangular) shape, as exemplified by the shapes shown in FIGS. 1-3, whose width to height ratio may vary, and with an edge cut possibly added (e.g. as shown as feature 31 in FIG. 3). In the shield shown in FIG. 1 there is a single domain 11 extending along the bottom ABS 12 (air bearing surface) edge of the shield and an opposing domain 13 along the top edge; this is referred to as a ‘2-domain’ state, because of its two primary longitudinal domains. In FIG. 2, a vertically oriented domain 21 is seen near the center of the shield, with opposing domains 22 and 23 on either side of 21. We refer to domain 21 as a ‘diamond, domain.’ In addition, a ‘3-domain’ state, as shown in FIG. 3, can occur as well as variations thereon.
Two types of problem relating to these configurations can occur in current shield designs: either the domain wall locations may be undesirable or the domain orientation may be undesirable. For example, there may be a desired repeatable orientation of the ABS domain with respect to the applied field. The present invention discloses a general solution to this problem, including a methodology for designing stable shields through control of their shapes.
The first of these approaches relates to domain configurations similar to that shown in FIG. 2. The vertically oriented diamond domain 21 in FIG. 2 can interfere with the response of the head, giving a response to an applied field that is different from that given by heads whose shields do not have such a domain (e.g. FIG. 1 or FIG. 3). The head's sensor element's response is sensitive to fringe fields emanating from the shield part adjacent to the sensor, so that shield domain differences can lead to differences in sensor response. The unfavorable domain orientation seen in FIG. 2 is nucleated by the parallel closure domains 22 and 23 that get locked into their parallel orientation during the initialization process.
The second problem, also solved by the new shield shapes disclosed here, is illustrated in FIG. 4. Here, even though there are no internal domains, there are two single domains 41 and 42 of opposite orientation—one along the top edge and one along the bottom edge. The problem is that opposite orientations can arise for different heads, or in the same head, for each re-initialization. The response of the head, especially its signal amplitude, will vary, depending on which of these two orientations it happens to be in.
A routine search of the prior art was performed with the following references of interest being found:
Headway application Ser. Nos. 11/117,672 filed Apr. 28, 2005 and 11/117,673 filed Apr. 28, 2005, disclose addition to a shield of a pair of tabs located at the edges closest to the ABS. These tabs serve to prevent flux concentrating at the edges so that horizontal fields at these edges are significantly reduced. Alternatively, the tabs may be omitted and, instead, outer portions of the shield's lower edge may be shaped so as to slope upwards away from the ABS.
U.S. Patent Application 2006/0203384 (Maruyama et al) teaches that the reversed trapezoidal shield shape has advantages, but proposes a method of forming a rectangular shape having the qualities of the reversed trapezoidal shape. U.S. Pat. No. 6,222,702 (Macken et al) shows a shield having a hexagonal shape and so designed that the W to H ratio provides an ideal magnetic domain structure and so that triangular shaped closure magnetic domains assure the domain walls do not move.
U.S. Patent Application 2007/0035878 (Guthrie et al) describes a notch in a trailing shield that helps align the main pole to the trailing shield. U.S. Patent Application 2006/0092566 (Ho et al) shows a shield in FIG. 6 that looks like the shield in FIG. 12 of the invention. U.S. Pat. No. 6,967,823 (Nokamoto et al) shows a main pole that has a trapezoidal shape. The shield has a domain stabilization layer.